Detection of transformed endothelial cells associated with survived cardiomyocytes in sub‐endocardial region of infarct myocardium

Previous studies have shown that cardiomyocytes in the sub‐endocardial region of infarct myocardium survive from ischemic injury. The present study was undertaken to explore a possible mechanism by which these cardiomyocytes survive in response to myocardial ischemia. Wild type mice (C57BL/6J, male, 8–10 weeks), or endothelial cell‐specific red fluorescent protein (RFP) expression transgenic mice ( Tie2CRE TdTomato ) were subjected to permanent ligation of left anterior descending of coronary artery along with sham‐operated controls in which the same surgery procedure was applied with an exception of the artery ligation. Pimonidazole was injected intravenously to define the hypoxic region, and lectin was injected to trace blood infiltration before sacrifice in all of the mice. The hearts were harvested on day one after the surgery and cut into serial sections for detection of cardiomyocytes and endothelial cells. The staining of pimonidazole showed that most of the infarct myocardium was under hypoxic condition except the sub‐endocardial region in which survived cardiomyocytes were detected. The RFP positive endothelial cells in the sub‐endocardial region also survived but displayed a suppressed expression of PECAM‐1 and VEGFR2. Correspondently, lectin infiltration analysis suggested blood leakage in the sub‐endocardial region although there was no blood infiltration in other regions of the infarct area. The results suggest that blood infiltration through the transformed endothelial cells in the sub‐endocardial region of infarcted myocardium would provide a non‐hypoxic microenvironment, contributing to the survival of cardiomyocytes in this region. Support or Funding Information West China Hospital, Sichuan UniversityThe changes of hypoxic microenvironment in the infarct myocardium region. Hypoxic condition (partial pressure of O 2 was less than 10 mmHg) was marked with hpi (pimonidazole) at 1 st day after ischemic injury. The blood infiltrations were reflected by FITC‐conjugated WGA through tail vein at 1 st , 4 th , 7 th day after LAD ligation. Hypoxic region stained by pimonidazole (red), and nuclear labeled by DAPI (blue). Abbreviations: DAPI, 4′,6‐diamidino‐2‐phenylindole; MI, myocardial infarction.The change of blood supplement in the sub‐endocardial region. The blood infiltrations were completely reflected by Lectin (FITC‐conjugated WGA) through tail vein at 1 st day after LAD ligation. Cardiomyocytes stained by TNNI3 (red), Blood infiltration labeled by FITC‐conjugated WGA (green), and nuclear labeled by DAPI (blue). Abbreviations: WGA, wheat germ agglutinin; DAPI, 4′, 6‐diamidino‐2‐phenylindole; MI, myocardial infarction.